1. Field of the Invention
The invention relates to circuits for detecting overdriving of radio frequency amplifiers.
2. Prior Art
In some applications separte radio frequency amplifiers are used to amplify the output of an amplitude modulated (AM) transmitter. For example, the output from a transmitter may not be sufficient for a particular application, such as for boating, aircraft, police communications, or amateur radio use, thus necessitating the use of a separate amplifier. Such amplifiers are commercially available including so-called "bilinear" amplifiers which amplify both the transmitted and received signal.
It is generally desirable to obtain as much output power as possible from these radio frequency amplifier. However, since the input to the amplifier (output of the transmitter) is not constant and varies with the amount of modulation and other variables, the amplifier can quite easily be overdriven. When this occurs, the output signal is clipped causing considerable distortion. It is thus desirable to know when the amplifier is being overdriven. Corrective steps may then be taken to present such overdriving; for example, the input signal level to the radio frequency amplifier may be reduced.
As will be seen, the presently disclosed circuit provides a relatively simple, inexpensive, yet very effective circuit for detecting an overdrive condition in a radio frequency amplifier.